1. Field of the Invention
The present invention relates to a light emitting device and a method for manufacturing the light emitting device.
2. Description of Related Art
Information and communication industry has become the current main stream industry, especially for various portable communication and display products, which have become the development priority. Because flat displays are a communication interface between human and information, the development of flat displays becomes critically important. Organic electro-luminescent displays are one type of light emitting device. Because of the advantages of self-luminance, wide view angle, saving power, simple process, low cost, wide operation temperature range, high response speed and full colorization, the organic electro-luminescent displays have a very good prospect and are expected to be the main stream of next generation flat displays.
The organic electro-luminescent displays are a type of display that displays by taking advantage of self-luminance characteristics of organic electro-luminescent materials, which includes a first electrode layer, a second electrode layer, and an organic electro-luminescent material sandwiched between the first electrode layer and the second electrode layer. When supplied with a direct current voltage, holes are injected from the anode into the organic electro-luminescent material, while electrons are injected from the cathode into the organic electro-luminescent material. The voltage level difference caused by the applied electric field causes the two types of carriers—the holes and electrons—to move and produce radiative recombination in the organic electro-luminescent material. A part of the energy released by the hole-electron recombination excites the organic electro-luminescent material molecules to form excited-state molecules. When the excited-state molecules fall back to a ground state by releasing energy, a proportion of the energy is released in the form of photons thus creating light. This is the emitting principle of the organic electro-luminescent displays.
Following the large-size development of the organic electro-luminescent displays, the bottom-neck researchers are facing is that the size of the mask used in the evaporation process for the organic electro-luminescent displays is limited. Therefore, a combination-type mask must be used for the evaporation process, i.e. multiple masks are combined with the gap between adjacent masks corresponding to the area between sub-pixels or corresponding to the sub-pixels. However, in manufacturing the combination-type mask, it is not easy to control the fabrication precision of the edge portion of the mask as well as the combination precision of the masks. As a result, fabrication cost of the mask is high and the evaporation process requires a long time.